A wild weekend is on the way for large parts of the South Island and lower North Island, with heavy rain and severe gales forecast.

Northwesterly winds were expected to become blustery over the South Island tomorrow morning, and over the lower North Island by evening, MetService said in a severe weather warning.

Severe gales were possible about inland parts of Otago and Canterbury tomorrow afternoon and evening, and in parts of Wairarapa and Hawke's Bay south of Hastings during Sunday.

Gusts may reach 120kmh in exposed places, with the possibility of 140kmh winds about the Tararua district and central Hawke's Bay on Sunday morning.

"Winds of this strength have the potential to damage trees, powerlines and unsecure structures and can make driving hazardous," MetService said.

It forecast rain becoming heavy over Fiordland tomorrow morning, and over south Westland in the afternoon.

Up to 150mm of rain could fall in the Fiordland ranges, with streams and rivers likely to rise quickly.

Today, traditionally the last day of Spring, dawned cold in many parts of the country, with MetService issuing snow warning for the Desert Road, and a fresh coating of powder appearing on the Mt Hutt skifield.

It also warned about the possibility of small hail showers between Wairarapa and Gisborne today, easing this evening. There was a low risk of thunderstorms in the area.

In Wellington, the temperature was not expected to top 13 degrees Celsius today, after managing to get above 20C on the five previous days.

The forecast maximum for Christchurch was 14C, for Timaru it was 13C and for Dunedin just 12C.

Along with showers, Hawke's Bay was also in for a drop in temperatures, compared to the highs in the mid-20s the region had previously this week. Today Napier was not expected to get above 17C, with Hastings to get no higher than 15C.

MetService duty forecaster Peter Knudsen said the lower temperatures were due to an outbreak of cooler air coming in from the south of the country.

Such events were not unusual at this time of year, and the cooler air was expected to be gone overnight.